The Small Gtpase, Rap1, Mediates Cd31-Induced Integrin Adhesion

Abstract

Integrin-mediated leukocyte adhesion is a critical aspect of leukocyte function that is tightly regulated by diverse stimuli, including chemokines, antigen receptors, and adhesion receptors. How cellular signals from CD31 and other adhesion amplifiers are integrated with those from classical mitogenic stimuli to regulate leukocyte function remains poorly understood. Here, we show that the cytoplasmic tail of CD31, an important integrin adhesion amplifier, propagates signals that induce T cell adhesion via β1 (VLA-4) and β2 (LFA-1) integrins. We identify the small GTPase, Rap1, as a critical mediator of this effect. Importantly, CD31 selectively activated the small Ras-related GTPase, Rap1, but not Ras, R-Ras, or Rap2. An activated Rap1 mutant stimulated T lymphocyte adhesion to intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM), as did the Rap1 guanine nucleotide exchange factor C3G and a catalytically inactive mutant of RapGAP. Conversely, negative regulators of Rap1 signaling blocked CD31-dependent adhesion. These findings identify a novel important role for Rap1 in regulating ligand-induced cell adhesion and suggest that Rap1 may play a more general role in coordinating adhesion-dependent signals during leukocyte migration and extravasation. Our findings also suggest an alternative mechanism, distinct from interference with Ras-proximal signaling, by which Rap1 might mediate transformation reversion.

Junctional Adhesion Molecule A Interacts with Afadin and PDZ-GEF2 to Activate Rap1A, Regulate β1 Integrin Levels, and Enhance Cell Migration

“…In in vitro studies, Rap1 has been reported to regulate integrin levels in epithelial cells (Mandell et al, 2005) as well as integrin activation in leukocytes (Reedquist et al, 2000). To verify these results in vivo, we determined the influence of JAM-A on ␤1 integrin protein levels and Rap1 activation in intestinal epithelial cells derived from JAM-A knockout mice.…”

Expression of Hypoxia-inducible Factor Prolyl Hydroxylase 3 HIFPH3 in Human Non-small Cell Lung Cancer (NSCLC) and Its Correlation with Prognosis

“…CD31 is found on the surface of platelets, monocytes, neutrophils, and some types of T-cells, and makes up a large portion of endothelial cell intercellular junctions (Albelda et al, 1991;Dejana, 2004). CD31 is involved in leukocyte migration (Muller, 1995), angiogenesis (DeLisser et al, 1997), and integrin activation (Bussolino et al, 1997;Reedquist et al, 2000). As a microvessel marker, CD31 is utilized to determine MVD.…”

The PI3K effector Arap3 interacts with the PI(3,4,5)P3 phosphatase SHIP2 in a SAM domain-dependent manner

“…We performed a co-immunoprecipitation with over-expressed proteins in either the presence or absence of RapV12, a constitutively active mutant of Rap1 [31], or of Rap1GAP, the GTPase activating protein specific for Rap, to reduce the amount of GTP-bound Rap1 [30]. We found that modulation of Rap1 activity did not affect the interaction between Arap3 and SHIP2 (Fig.…”

“…The GST-tagged SAM domains of Arap3 (residues 1-75) and SHIP2 (residues 1192-1258) were made by inserting SalI/ NotI-digested PCR products into XhoI/NotI-digested pGEX4T3 vector (Pharmacia). HA-RapV12 and HA-RapGAP were described previously [30,31].…”